The bending and tempering of glass sheets is generally well-known in the art. It has become common practice to bend and temper relatively thick sheets of glass e.g., 1/4" thickness and greater; however, the conventional methods are not well suited for the bending and especially the tempering of thin sheets of glass.
There is developing a rapidly expanding demand for extremely thin, formed and tempered glass sheets e.g.. 1/8" thickness and less, for use in special laminated windshields, convertible backlights and elsewhere, particularly in the automotive market.
Formed and tempered glass sheets are typically manufactured in a generally continuous process in which a glass sheet is heated in a furnace to its plastic or softening temperature; next, shaped to the desired configuration by press or gravity bending; thereafter, passed through a tempering station in which blasts of air impinge against the surfaces of the formed glass sheet; and finally discharged for further cooling. Conventional tempering methods for thick glass sheets typically include passage of the formed glass sheet through the tempering section on a roller conveyor, during which air is directed onto the top surface of the formed glass sheet, and simultaneously onto the bottom surface of the glass sheet between the rollers. However, thin, formed glass sheets are amenable to deformation during transfer from the forming step through at least the initial stages of tempering, due to the effects of gravity, contact with the roller conveyor and the force of the air blasts on the still-plastic thin glass sheets immediately prior to tempering.
Accordingly, shuttle mechanisms have been devised for receiving thin, formed glass sheets from a forming station and conveying them through a tempering station. Generally, these shuttle devices support the formed glass sheets near the peripheral edges thereof, while conveying the sheets through the tempering station. In this fashion, the conformation of the formed glass sheets is maintained during tempering, and substantially the entire underside of the formed glass sheets is exposed to the tempering air blasts.
U.S. Pat. No. 3,607,200 discloses a vacuum assisted bending apparatus, wherein a shaping frame lifts a glass sheet into engagement with a vacuum mold, presses the glass sheet against the mold, then transfers the formed glass sheet into a cooling section where it is unloaded onto a device for oscillating the formed glass sheet while being cooled. The shaping frame is therefore utilized in both the forming step and the shuttling of the formed glass sheet into the cooling section. Because the formed glass sheet is transferred to an oscillating device in the cooling section which does not provide support only at the marginal peripheral edges of the sheet, the formed glass sheet is subject to deformation thereafter until it is sufficiently cooled below its plastic set temperature.
U.S. Pat. No. 4,092,141 discloses a support ring which receives a formed glass sheet previously held by vacuum on the underside surface of an upper forming mold. The support ring, having the formed glass sheet deposited thereon, is then transported to a tempering station, where the formed glass sheet is unloaded from the support ring onto elevator rolls prior to being fully tempered. Again, distortion of the formed glass sheet may occur as a result of removing it from the support ring while above its plastic set temperature.
U.S. Pat. No. 4,364,765 discloses a carrier mold ring which receives a partially formed glass sheet from the underside surface of a vacuum holder in a furnace, the glass sheet thereafter being fully formed by gravity while contained within the carrier mold ring. The carrier mold ring then transports the formed glass sheet into a tempering zone where the glass is lifted from the carrier mold ring by upward air blasts. The carrier mold ring not only carries the glass sheet, but additionally participates in its molding or shaping.
U.S. Pat. No. 3,684,473 discloses a bending mold which lifts a heated glass sheet, and by the forces of gravity and inertia forms the glass sheet into the desired configuration. The bending mold, supporting the formed glass sheet on the peripheral marginal edges thereof, passes into a tempering zone, and thereafter deposits the formed and tempered glass sheet onto a take away roller conveyor.
U.S. Pat. No. 3,846,104 discloses a method and apparatus wherein a formed glass sheet is released from the undersurface of an upper vacuum mold onto a tempering ring which supports the formed glass sheet at the marginal edges thereof, and thereafter the tempering ring is passed through a cooling section. The tempering ring is laterally positioned to accept the formed glass sheet after the lower shaping mold has retreated from the upper vacuum mold, thereby extending the elapsed time between the forming and cooling operations.
Finally, U.S. Pat. No. 4,339,259 discloses a process whereby a lower mold ring presses a glass sheet against the undersurface of an upper bending mold, and thereafter transports the formed glass sheet through a tempering zone; the parting of the upper mold away from the lower mold ring and the traverse of the lower molding ring through the tempering zone occurring so as to maintain the same elevation of the lower mold ring throughout.